What did Luke mean by 'out of every nation under heaven' in Acts 2:5?
Luke meant Jews from every nation in the then-known world, not Gentiles. These were devout Jews living in Gentile nations from Great Britain west to India east, who had Jewish communities. They traveled to Jerusalem for the feast, speaking various languages.
Les explains that these Jews had been living in Gentile nations and had picked up those languages, so their children were raised under them and may have almost forgotten Aramaic and Hebrew. They came to Jerusalem speaking the languages of the nations to the east, northern Africa, Greece, Italy, Spain, and Great Britain. He says 'out of every nation under heaven' means every nation in the then-known world, from Great Britain on the west to at least the western part of India and the Indus River on the east, all of which had Jewish communities. The word 'devout' indicates practicing Jews who would spend the money and take the time to return for the feast. There were thousands of them.
And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven.
More Questions
Why were there Jews from every nation under heaven in Jerusalem at Pentecost in Acts 2:5?
The reason Acts 2:5 can speak of Jews dwelling in Jerusalem from every nation under heaven is that Jews had been migrating throughout the known world since 606 B.C., so that they were scattered into every nation.